This invention relates to modem architecture for communication lines. More particularly, this invention relates to modem circuitry used in connection with isolation systems for connecting to phone lines.
New generations of consumer appliances like set-top boxes, payphones, vending machines and other systems often require or prefer low-speed data modems. Such modems allow remote hosts to handle billing or other housekeeping functions, or permit xe2x80x9csmartxe2x80x9d vending machines to call for more supplies. Although typical microprocessor and digital-signal-processor (DSP)-based multimedia chips employed in set-top boxes and other systems are capable of implementing a low-speed modem, they would do so at an undesirable manufacturing complexity and expense.
Prior modem architectures typically included multiple integrated circuits for handling modem processing and communication line termination. In particular, one or more digital-signal-processor chips have been coupled to analog-front-end circuitry, which in turn has been connected to line termination circuitry across a transformer isolation barrier. Such modem architectures suffer from numerous disadvantages.
The present invention provides an improved modem architecture and associated method that integrate modem functionality and line-side isolation functionality while also providing a modem interface that allows command and data mode control.
In one embodiment, the present invention is an integrated modem and line-isolation circuit with modem command mode and data mode control including system-side line-isolation circuitry capable of being coupled to an isolation barrier, digital signal processing (DSP) circuitry integrated with the system-side line-isolation circuitry, the DSP circuitry having a modem processor for modem data and a digital processor for system-side circuitry; and a serial input pin that receives an M-bit word, wherein M-minus-N bits of the M-bit word are data bits and N-bits of the M-bit word are control bits. The control bits serve to identify whether the modem processor should process the M-bit word in command mode or in data mode. In a more particular embodiment, the M-bit word may be a 9-bit word with 8 bits being for data and 1-bit being for control, and this single control bit may be the last bit of the 9-bit word received through the serial input pin. In addition, the serial input pin may receive a start bit before receiving the M-bit word and a stop bit after receiving the M-bit word. Still further, the digital processor may include digital filters for digital data received across the isolation barrier from the communication line and a digital modulator for digital data transmitted across the isolation barrier to the communication line. Furthermore, the system-side line-isolation circuitry may provide system-side phone line direct access arrangement functionality.
In another embodiment, the present invention is a method for controlling whether modem circuitry within an integrated modem and line-isolation circuit operates in command mode or data mode including receiving an M-bit word through a serial input pin, utilizing N-bits of the M-bit word as control bits, and determining whether the modem circuitry operates in command mode or data mode based upon the state of the N control bits. In a more particular embodiment, the M-bit word may be a 9-bit word with 8 bits being for data and 1-bit being for control. Still further, the serial input pin may be part of an asynchronous serial interface.
In a further embodiment, the present invention is a method for providing modem command mode and data mode control for a modem and line-isolation integrated circuit including providing a system-side line-isolation integrated circuit including digital-signal-processing (DSP) circuitry having a modem processor for modem data and a digital processor for system-side circuitry, providing a serial input pin for the system-side line-isolation integrated circuit, receiving an M-bit word through the serial input pin, utilizing N-bits of the M-bit word as control bits, and determining whether the modem processor operates in command mode or data mode based upon the state of the N control bits. In a more particular embodiment, the method may also include communicating digital information through an isolation barrier between the system-side line-isolation integrated circuit and a line-side line-isolation integrated circuit.